Invalidation of a Target Realm in a Realm Hierarchy

2. The apparatus according to claim 1, wherein the processing circuitry is prohibited from entering a given child realm from a realm other than the parent realm of the given child realm.

3. The apparatus according to claim 1, wherein the realm management circuitry is configured to store realm management data associated with a given child realm in a memory region owned by the parent realm of the given child realm.

4. The apparatus according to claim 1, wherein the realm management circuitry is configured to trigger a reclaim operation for reclaiming each memory region owned by the invalidated target realm.

6. The apparatus according to claim 1, wherein in response to a region claim command requesting transfer of ownership of a target memory region to a given child realm, the realm management circuitry is configured to reject the region claim command when the target memory region is owned by a realm other than the parent realm of the given child realm.

7. The apparatus according to claim 6, wherein each memory region is associated with one of a plurality of lifecycle states, and the realm management circuitry is configured to reject the region claim command when the target memory region is in a lifecycle state other than a predetermined lifecycle state.

8. The apparatus according to claim 1, wherein a given child realm has a right to exclude its parent realm from accessing data stored in a given memory region owned by the given child realm.

9. The apparatus according to claim 8, wherein the memory access circuitry is configured to determine, in dependence on an attribute set by the given child realm, whether its parent realm is allowed to access data stored in the given memory region owned by the child realm.

10. The apparatus according to claim 9, wherein when the given child realm allows its parent realm to access data stored in the given memory region, a sibling realm sharing the same parent realm as the given child realm is also allowed to access the data stored in the given memory region.

11. The apparatus according to claim 1, wherein the memory access circuitry is configured to permit any realm to access data stored in the given memory region owned by the child realm when a global visibility attribute set by the given child realm has a predetermined value.

13. The apparatus according to claim 1, wherein the realm management circuitry comprises a hardware unit.

14. The apparatus according to claim 1, wherein the realm management circuitry comprises the processing circuitry executing realm management software.